This invention relates to modulators of antiskid devices for air brakes of motor vehicles, and more particularly it is concerned with a modulator of an antiskid device for air brakes of the type wherein a throttling signal is produced by a computer to change the braking pressure from a rapid pressure increase state to a slow pressure increase state before the braking pressure reaches a pressure increase target value, a pressure reducing electric signal is produced to rapidly reduce the braking pressure when the braking pressure has reached the pressure increase target value, and a throttling signal is produced again to change the braking pressure from a rapid pressure decrease state to a slow pressure decrease state before the braking pressure reaches a pressure decrease target value.
In one type of modulator of an antiskid device for air brakes of the prior art, the modulator is actuated by a pressure reducing electric signal which is produced by the computer to discharge pressurized air from the brake actuators when the braking pressure applied by the brake actuators has reached a pressure increase target value, and pressure air is supplied to the brake actuators again as the pressure reducing electric signal is turned off when the braking pressure has reached a pressure decrease target value. In this type of modulator, there is a time lag of the initiation of a decrease or increase in the braking pressure caused by the operation of the modulator behind the turning on or off an electric signal. This has hitherto caused a rise or a fall in the braking pressure applied by the brake actuators to an unnecessarily high or low level, with the result that skidding of a moderate degree has occurred or the braking force has not been high enough, making it impossible to smoothly control the braking of the wheels.